Brain, Lissencephaly Type 2

Lissencephalies (“smooth brain”) are a group of rare brain disorders characterized by a loss of gyri and sulci, leading to a smooth external appearance. Type 2, or cobblestone, lissencephaly is usually associated with cerebellar and ocular abnormalities and congenital muscular dystrophy; these features define a family of syndromes, e.g. Walker-Warburg syndrome, and are due to genetic defects in glycosylation. Microscopically, the brain shows features of neuronal over-migration beyond the glia limitans: the cortex is highly disorganized, without signs of lamination; there is no preservation of the molecular layer; large-calibre leptomeningeal vessels become buried within the brain parenchyma. Over-migration also results in fusion across the midline, as seen in the dorsal and ventral frontal lobes in this case.